1. Field of the Invention
The present invention relates to an ink-jet recording process, and particularly to an ink-jet recording process that can provide a high-quality color image high in fixing ability on plain paper.
2. Related Background Art
An ink-jet recording method is such a method that recording is conducted by ejecting minute droplets of an ink to apply the ink to a recording medium such as paper. According to the method (see, for example, Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914), in which an electrothermal converter is used as an ejection energy-supplying means to apply thermal energy to ink so as to generate bubbles, thereby ejecting droplets of the ink, the formation of a high-density multi-orifice in a recording head can be realized with ease, and high-resolution and high-quality images can be recorded at high speed.
However, the conventional inks used in ink-jet recording generally comprise, as a principal component, water, and additionally include a water-soluble high boiling solvent such as glycol for the purpose of preventing drying and clogging at orifices, and the like. When such an ink is used to conduct recording on plain paper, there have hence arisen such problems as fixing ability cannot be sufficiently achieved, and image irregularity occurs, which appears to be attributed to the uneven distribution of a filler and/or a size on the surface of the paper. In particular, when color images are intended to be formed, plural inks of different colors are overlapped one after another before they are fixed to paper. Therefore, color bleeding and uneven color mixing have occurred at portions of boundaries between images of different colors (this phenomenon will hereinafter be referred to as “bleeding” simply), resulting in a failure to obtain satisfactory images.
As a means for improving the bleeding, the addition of a compound capable of enhancing penetrability, such as a surfactant, into the inks is disclosed (see, for example, Japanese Patent Application Laid-Open No. 55-65269). According to this method, the penetrability of the inks into recording paper is improved, and so bleeding can be prevented to some extent. However, such disadvantages that the image density and brightness of the resulting image are lowered, and the image shows through a recording medium to the back side thereof have been involved because coloring materials contained in the inks penetrate deeply into the recording medium. In addition, such inks have not been preferred because they are easy to be spread due to the improvement of wettability on the recording medium, resulting in reduction of resolution and occurrence of feathering.
In order to solve the above-described problems, there have been further proposed various methods, in which a liquid, which can make the quality of an image better, is applied to a recording medium prior to ejection of an ink. For example, a method, in which a solution of a polymer such as carboxymethyl cellulose, polyvinyl alcohol or polyvinyl acetate is ejected, and printing is then conducted, has been proposed (see, for example, Japanese Patent Application Laid-Open No. 56-89595). However, according to this method, it is feared that a problem that fixing ability is lowered due to poor drying ability of the solution itself will arise though anti-bleeding property is improved. In order to solve this problem, there have been disclosed, for example, a method, in which a liquid comprising an organic compound having two or more cationic groups per molecule is applied to a recording medium, and recording is then conducted with an ink comprising an anionic dye (see, for example, Japanese Patent Application Laid-Open No. 63-29971), a method, in which an acidic liquid containing succinic acid or the like is applied to a recording medium, and recording is then conducted with an ink comprising an anionic dye (see, for example, Japanese Patent Application Laid-Open No. 64-9279) and besides a method, in which a liquid, which insolubilizes dyes, is applied to a recording medium prior to recording (see, for example, Japanese Patent Application Laid-Open No. 64-63185).
According to all these methods, bleeding is prevented to some extent. In these methods, however, a color ink is applied to a recording medium at a stage after the reaction liquid penetrates into the recording medium and is present within the recording medium, and no reaction liquid becomes present on the surface of the recording medium, so that almost all the reaction takes place in the recording medium. Therefore, a problem that the coloring property of the resulting image is not improved, and a problem of the show through that the coloring material is shown through from the back side of the recording medium have arisen. As described above, when the color ink is reacted with the reaction liquid at the time the reaction liquid is present on the recording medium, the fixing ability of the resulting image is deteriorated. When the reaction liquid is reacted with the color ink at the time the reaction liquid is present in the recording medium on the other hand, it is feared that a problem that coloring property is deteriorated will arise.
To prevent bleeding by utilizing a reaction of a polyvalent metal ion with a carboxyl group has also been proposed (see, for example, Japanese Patent Application Laid-Open No. 5-202328). Even in this case, a liquid containing the polyvalent metal ion is reacted with a color ink after a recording medium is impregnated with the liquid, so that bleeding is prevented to some extent. However, problems of deterioration of coloring property and the show through are feared when the penetrability of the color ink into the recording medium is high. When the penetrability is low to the contrary, it is feared that a problem that fixing requires a long time may arise. In addition, a method, in which anti-bleeding property is improved by a reaction among a pigment, a resin emulsion and a polyvalent metal salt, has also been proposed (see, for example, Japanese Patent Application Laid-Open No. 9-207424). The fundamental concept of this method is almost the same as Japanese Patent Application Laid-Open No. 5-202328.
Further, an ink-jet recording method, by which an optimized image is obtained by defining an amount of a reaction liquid applied in terms of its weight ratio to an amount of a color ink applied, has been proposed (see, for example, International Publication No. 98/30398, pamphlet). In this method, it has been proposed to make a dot of the reaction liquid smaller than a dot of the color ink though conditions are substantially changed by surface tensions of the reaction liquid and color ink. According to this method, however, the amount of the reaction liquid applied must also be increased as the color becomes a secondary color or tertiary color. As a result, a larger amount of a solvent comes to be present in printed areas of the secondary color and tertiary color, so that fixing requires a longer time.
As described above, various proposals using the color ink and reaction liquid as a means for improving the anti-bleeding property have been made. In all events, the anti-bleeding property is improved to some extent, but the deterioration of coloring property and the show through occur when importance is attached to the fixing ability. On the other hand, the fixing ability is deteriorated when importance is attached to the coloring property and the show through. In other words, under the circumstances, any method that can satisfy the fixing ability and the coloring property and the show through at the same time while reducing the bleeding has not been proposed. Further, the proposal that the amount of the reaction liquid applied is defined is a proposal that its ratio to the amount of the color ink applied is specified, so that the proposal cannot be always be said to be optimum according to the recording method and conditions.